School of Biosciences

Prof Vladimir Buchman
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MD PhD

Current major projects

Synuclein biology

Synucleins came into the limelight in 1997 after the first studies have been published linking missense mutations in the SNCA, a gene encoding alpha-synuclein, to a familial form of Parkinson’s disease, and aggregation of alpha-synuclein to histopathological changes typical to the majority of Parkinson’s disease cases. Despite the high level of interest triggered by these findings, neither normal function of alpha-synuclein, nor the exact mechanism of pathological changes caused by its dysfunction are well understood. Even less is known about the function of two other members of the family, beta-synuclein and gamma-synuclein, in health and disease. The research community still encounters difficulties with interpretation of the results obtained in many laboratories using various experimental systems, mainly due to unconventional structural properties of synucleins, their involvement in multiple intracellular processes, differential effect of various protein isoforms (monomers, oligomers, protofibrils and fibrils) on these processes and functional redundancy within the family. Therefore, further detailed studies of all aspects of synuclein biology in more appropriate experimental systems are vital for the understanding of the role of these proteins in normal and degenerating nervous systems. Currently, we are involved in several projects that might help to achieve these goals:

• Normal function of synucleins i. In synaptic transmission Recently, we have produced mice lacking members of the synuclein family in all possible combinations (single, double and triple knock-outs) and employed these models to reveal the importance of these proteins in modulation of neurotransmitter release in various types of neurons (for example see Figure 1). We also have evidence of synucleins involvement in neurotransmitter uptake by presynaptic vesicles and are currently studying the exact mechanism of this effect.

ii. In the development of midbrain dopaminergic neurons. Our previous results suggested differential role for synuclein family members in this process, and the existence of certain mechanisms that might compensate for the dysfunction of these proteins during critical developmental periods. Currently, we are studying how these changes may affect sensitivity of adult dopaminergic neurons to various neurotoxic challenges.

iii. In mitochondria energy production. Although synucleins were always considered to be involved in normal function of brain mitochondria, it is still not clear what elements of the energy production chain might be modulated by these proteins. To address this question, we apply various biochemical, biophysical and pharmacological methods to assess the effects of each synuclein on mitochondrial function. These studies are carried out on purified mitochondria, neuronal cell cultures and brain slices obtained from various synuclein knock-out mice. We also reintroduce synucleins into cultured neurons by lentiviral delivery, or by adding functional monomeric recombinant synucleins to in vitro reactions.

iv. In adipocyte biology (gamma-synuclein). In addition to robust expression in the nervous system, particularly in periphery sensory and lower motor neurons, gamma-synuclein is abundant in white adipose tissue. We have demonstrated dietary regulation of gamma-synuclein expression in adipocytes and rescue of mice from high fat diet induced obesity and metabolic phenotype by knocking-out the gamma-synuclein gene. Our data support the hypothesis that gamma-synuclein depletion increases the level of lipolisis in adipocytes in conditions of nutrient excess, possibly by the modulation of ATGL activity and lipid droplet fusion (Figure 2). Ongoing detail studies of these mechanisms should reveal if gamma-synuclein can be considered as a promising target for therapy of obesity and metabolic syndrome.

• Synucleins in pathological processes. i. Cytotoxicity of alpha-synuclein aggregation intermediates. We study the toxicity of various intermediates or final products of purified recombinant alpha-synuclein aggregation to various types of neurons, including neurons from synuclein knock-out mice. These alpha-synuclein species are also used to assess their effects on the function of mitochondria, as described above.

ii. Toxic gain-of-function of gamma-synuclein in motor neurons and its role in motor neuron disease. Recently, we have described novel gamma-synuclein-positive pathological profiles in the cortico-spinal tract of a subset of ALS patients. We suggested that these structures represent aggregates of gamma-synuclein formed in degenerating axons of upper motor neurons, and therefore, pathological aggregation of gamma-synuclein might be involved in pathogenesis of certain forms or stages of the disease. Consistently, mice overexpressing wild type mouse gamma-synuclein in neurons develop age- and gene dose-dependent motor phenotype caused by the aggregation of gamma-synuclein in neuron cell bodies and axons followed by selective degeneration of certain motor neuron populations (Figure 3). Our next goal is to reveal the chain of events leading to neuronal dysfunction and death in this model of ALS and clarify the origin and composition of pathological gamma-synuclein-positive profiles in the nervous system of ALS patients.

iii. Age-dependent depletion of functional synucleins from neuronal synapses and its contribution to compromised neurotransmission. It is feasible that massive pathological aggregation of alpha-synuclein in neuron cell body and axons of Parkinson’s and Lewy body disease patients leads to profound depletion of presynaptic terminals from functional alpha-synuclein. This might compromise normal synaptic neurotransmission and contribute to the manifestation of disease symptoms. In mice constitutive knock-out of the gene this effect can be neutralised by certain compensatory mechanisms during critical periods of the development (see above). To leapfrog this, we have recently produced mice in which the alpha-synuclein gene can be conditionally inactivated in selected neuronal populations and at any developmental stage, including ageing animals (Figure 4). Studies of these mice shall reveal a role of functional alpha-synuclein deficiency in the development of symptoms typical for synucleinopathies.

iv. Gamma-synuclein in tumourigenesis and malignisation. In addition to neural and white adipose tissues, abundant gamma-synuclein is often found in certain types of tumours, particularly at advance stages of malignisation. This phenomenon has not been properly studied, but it has been suggested in literature, that gamma-synuclein is involved in the progression of mammary gland tumours. We observed a correlation between expression of gamma-synuclein and Erb2B in this type of tumours and tumour cell lines. However, our studies of Erb2B-induced mammary tumourigenesis and metastasis in the presence and absence of gamma-synuclein demonstrate that this protein is not required for either of these processes, at least in this type of tumours. Further studies should reveal why gamma-synuclein becomes a marker of certain advance stage tumours.

Relationship between RNA metabolism and pathological aggregation of RNA-binding proteins in the development of ALS and related diseases A significant number of ALS-associated mutations has been identified in genes encoding RNA-binding proteins. Moreover, some of these proteins possess prion-like domains that are responsible for their high propensity to aggregate. Consistently, pathological aggregates formed by these proteins were found in the nervous system of both familial and sporadic ALS and certain other neurodegenerative diseases. Thus, both compromised RNA metabolism and pathological protein aggregation are considered as potential causes of neurodegeneration, but contribution to the development of pathology and relationship between these processes are not yet well understood. To clarify this, we currently employ various cell and animal models to study FUS, one of RNA-binding proteins involved in pathogenesis of ALS and related diseases, and plan to extend these studies to other RNA-binding proteins that have been very recently linked to these diseases, namely hnRNPA1 and hnRNPA2/B1.

• Mechanism of pathological aggregation of FUS protein in cells. Our studies of intracellular localisation and formation of atypical structures (small or larger puncta, aggresomes, etc.) by various modified forms of human FUS protein in a number of stable cell lines, have demonstrated that FUS becomes highly aggregation-prone when it is not able to bind target RNA (Figure 5). Based on these observations, we suggested a hypothesis of pathological aggregation of FUS (manuscript under review).

• Animal models of FUSopathies. To extend our studies of FUS aggregation to a more relevant in vivo system, we have produced transgenic mice expressing C-terminally truncated form of human FUS in their neurons. These mice abruptly develop severe motor pathology at the age of 2.5 – 4.5 months, characterised by profound aggregation of both human and endogenous mouse FUS in all neuronal compartments, and severe damage of selected populations of motor neurons and their axons (paper in press). Other mouse lines expressing different variants of FUS has also been produced, and studies of their phenotypes are underway.

• Physiological and pathological sequestering of FUS and other aggregation-prone RNA-binding proteins in nuclear and cytoplasmic RNP complexes. These proteins are residents of various nuclear and cytoplasmic RNP complexes in normal cells and their abilities to associate with these complexes are often compromised in degenerating neurons. However, the function of each protein in each RNP complex is not clear. The aim of our studies is to reveal these functions and link them with pathological changes in ALS and other neurodegenerative diseases.

Repeat expansions in the C9ORF72 genomic locus as aetiological factor for ALS and related diseases Expansion of GGGGCC repeats in the C9ORF72 locus is the most common mutation in ALS patients, but molecular mechanisms of pathology development are still elusive. In collaboration with colleagues from the Institute of Neurology, Kings College London, and the Sheffield Institute for Translational Neuroscience, we study the effects of the repeat size on the onset, clinical manifestations and other parameters of the disease, (Figure 6).

Functional domains of neurospecific transcriptional modulators belonging to the d4/DPF/BAF45 family Three genes comprise the d4 family of transcriptional modulators, but alternative promoters and splicing events produce a large variety of encoded proteins with different composition of structural domains. Neurospecific members of the d4 protein family (neuro-d4/BAF45b and cer-d4/BAF45c) are components of a large chromatin remodelling complex in differentiated neurons. Existing data suggest that developmental switch from neuronal progenitor cells to committed neurons requires substitution of a slightly related BAF45a protein to d4 proteins in this complex. We study the role of various structural domains of d4 proteins in interaction with components of chromatin and phospholipids. We have also produced mice expressing only C-terminally truncated, i.e. lacking important double PHD finger domains, versions of neuro-d4/BAF45b and cer-d4/BAF45c proteins. Although both single and double mutant mice are viable, the latter develop certain behavioural abnormalities.